1. Field of the Invention
The present invention relates to a corona discharge apparatus.
2. Description of the Related Art
Corona discharge apparatuses have been widely used to form irregularities, on the order of a micron, on the outer surface of a work object. Such a corona discharge apparatus can also be used to modify the outer surface of a work object.
Various corona discharge apparatuses for modifying the outer surface of a work object are known from, for example, Japanese Unexamined Patent Publication Nos. 6-163143, 8-081573, 10-241827, 10-309749, 11-060759 and 11-279302. One of the corona discharge apparatuses that have been available on the market comprises a discharge unit having a pair of electrodes disposed so that they face each other. While applying a discharge with a high voltage to the electrodes, a gas stream is injected between the electrodes to generate an arc-shaped corona discharge between the electrodes. This produces a plasma around the corona discharge. The plasma is applied to the work object in order to modify its surface qualities or its surface properties. The modification of the qualities and properties of the outer surface of the work object is performed by activating the outer surface of the work object with the plasma. As disclosed in Japanese Unexamined Patent Publication No. 6-163143, the plasma treatment is suitable for modification of surfaces of many materials such as plastics, paper, metals and ceramics.
The following examples are practical applications of plasma treatment:
(1) Applying plasma treatment to plastics, paper, metals or glass before printing on them. This increases adhesion of the print ink to the surface of the material.
(2) Applying plasma treatment to films before applying a binder to them. This increases adhesion of the binder to the surface of the film.
(3) Applying plasma treatment to base substances before coating them. This increases adhesion of the coating film with the surface.
(4) Applying plasma treatment to a work object transforms organic matter, which is a source of smudges, into H2O and CO2. This removes smudges from the surface of the work object.
A corona discharge apparatus of this kind is generally configured such that a high discharge voltage is applied to a discharge unit from a control unit, including a high-voltage transformer circuit, through a high-tension cable. The high-tension cable is usually connected to the control unit and the discharge unit to electrically couple them together. Typically, it is cumbersome to manage the high-tension cable since the high-tension cable is made of a wire that is thicker than general electric wires and communication cables. It is also difficult to manage the high-tension cable because a firm sheath that protects it against breakage surrounds the wire.
Further, the high-tension cable that electrically couples the control unit and the discharge unit together has to have a sufficient extension length when the corona discharge apparatus is set up in a working site or a factory so that the discharge unit can be located adjacent to the work object. On the other hand, when considering where to locate the units from the standpoint of the factory, it is necessary to consider the length and maneuverability of the high-tension cable to determine the locations for the discharge unit and the control unit.
It is therefore an object of the present invention to provide a corona discharge apparatus including a connecting cable between a control unit and a discharge unit that is convenient and easily manageable.
It is another object of the present invention to provide a corona discharge apparatus that is flexible and allows installation of the control unit and the discharge unit in various work sites.
The foregoing objects of the present invention are accomplished by a corona discharge apparatus which comprises a discharge unit comprising a discharge electrode assembly having at least two discharge electrodes and high-voltage generation means for generating a high voltage. The high-voltage generation means is connected to the discharge electrode assembly for applying the high-voltage to the discharge electrodes and causing the discharge electrodes to generate a corona discharge. The apparatus also includes a control unit, separate from the discharge unit, for controlling the discharge unit. An electric cable which is detachably connected to at least one of the discharge unit and the control unit so as to electrically couple the discharge unit to the control unit.
The corona discharge apparatus thus configured has the discharge unit with the high-voltage generation means installed therein. The discharge unit and the control unit can be electrically coupled together by an ordinary cable comprising a power supply wire and a signal communication wire. This avoids connecting them together by means of a high-tension cable as was previously done. As a result, the manageability and maneuverability of the cable connecting the control unit and the discharge unit are significantly improved. Moreover, since the cable is detachable from both units, it is possible to connect the two units by a cable having a length that meets the actual conditions of the work site.
According to a preferred embodiment of the present invention, the corona discharge apparatus is adapted to generate an arc-shaped corona discharge between the discharge electrodes by applying a high voltage to the discharge electrodes while passing a gas between the discharge electrodes. This produces plasma around the corona discharge which is applied to the work object to modify a surface of the work object. The corona discharge apparatus comprises a discharge unit provided with the discharge electrodes and a high-voltage generation circuit for generating and applying a high voltage to the discharge electrodes so as thereby to generate the corona discharge. The corona discharge apparatus also comprises a control unit for controlling the discharge unit. The discharge unit and the control unit are both provided with connectors that allow a cable to be detachably connected to the discharge unit and the control unit. The cable electrically couples the discharge unit to the control unit. The discharge unit is also provided with a connector that allows a gas guide tube extending from a gas supply source to be detachably connected to the discharge unit.
The gas supply source, such as an air pump, an air blower, an air compressor and a gas bottle, may be installed in the control unit. In this case, the control unit is provided with a connector for detachably connecting the gas guide tube so that feed air can be supplied from the gas supply source to the discharge unit. The discharge unit is preferably provided with a gas flow sensor disposed in a gas flow passage in the discharge unit. The control unit is provided with control means that receives a signal representative of a gas flow rate from the gas flow sensor. The control unit provides feedback control to the gas supply source on the basis of the gas flow rate signal so as to maintain the gas injected through a gas outlet port of the discharge unit at a constant rate. This control system provides a constant rate of gas flow regardless of the length of the gas guide tube.
According to another preferred embodiment of the present invention, the discharge unit is provided with a temperature sensor installed therein to detect an internal temperature of the discharge unit. The control unit receives a signal representative of the internal temperature from the temperature sensor and controls the discharge unit, namely the high-voltage generation circuit, to control generation of high voltage on the basis of the internal temperature signal. Specifically, the control unit prohibits the high-voltage generation circuit from generating a high voltage when the internal temperature exceeds a predetermined upper limit temperature of, for example, 80xc2x0 C. and/or a predetermined lower limit temperature of, for example xe2x88x9280xc2x0 C. Prohibiting the high-voltage generation circuit from generating a high voltage when the interior of the discharge unit is higher than the upper limit temperature prevents a high-frequency step-up transformer from causing heat-deterioration. The high-frequency step-up transformer forms part of the high-voltage generation circuit and is generally sensitive to heat. Prohibiting the high-voltage generation circuit from generating a high voltage when the interior of the discharge unit is lower than the lower limit temperature prevents the discharge electrodes from causing an accident such as a short-circuit when frost forms on the discharge electrodes in cold weather.